Analysis of electronic contributions to the vibrational frequency of CO/Cu2O(111)

The change in the CO vibrational frequency after adsorption on low-coordina ted copper atoms at the Cu2O(111) surface has been studied theoretically wi th gradient-corrected density-functional theory (DFT) methods. The surface was modeled with a Cu28O14 cluster embedded in point charges and total-ion model potentials. An analysis of the contributions to changes in the CO str etching mode based on the electron density was performed. We show that the proper description of the Cu 3d-->CO 2 pi* back donation, which is responsi ble for the experimentally observed small red shift, requires the inclusion of electron correlation in a self-consistent way. In addition to this main physical effect, the absolute value of the frequency shift depends on the form of the exchange functional and on the description of electrostatic int eractions in the cluster model. (C) 1999 Elsevier Science B.V. All rights r eserved.